Method and system for determining a tyre load during the running of a motor vehicle

ABSTRACT

A method for determining a load exerted on a tyre, fitted on a vehicle, during running of the vehicle on a rolling surface, is disclosed. The method includes acquiring a first signal comprising a first signal portion representative of a radial deformation; measuring an amplitude of the radial deformation in the first signal portion; estimating a rotation speed of the tyre corresponding to the radial deformation; estimating an inflation pressure of the tyre corresponding to the radial deformation; and deriving the load exerted on the tyre from the amplitude, the rotation speed, and the inflation pressure. The first signal portion is representative of the radial deformation to which a first tread area portion of the tyre is subjected during passage of the first tread area portion through a contact region between the tyre and the rolling surface. A system for determining the load exerted on the tyre is also disclosed.

The present invention relates to a method and a system for determining avertical load to which a tyre mounted on a vehicle is subjected, duringrunning of the vehicle.

Inflation pressure is a convenient measurement to make on a tyre fittedon a vehicle wheel and it is becoming a standard by which tyres aremonitored. Tyre load, i.e., the supported weight, is a more difficultmeasurement but, unlike pressure, is a direct measurement of tyrestress. Tyres are selected for a particular vehicle based on thephysical strength of their structure and/or material, as well as on thenormal range of vehicle weight that they should support at specifiednominal temperature and pressure. If the vehicle applies a load to atyre in excess of the load range for which the tyre has been designed,the tyre is subjected to excessive stress and may fail or have itsexpected lifetime shortened.

Furthermore, it has to be considered that tyre maintenance is mainlybased on the duty, by the vehicle driver, of maintaining tyre pressurenear a nominal value, defined by the vehicle and tyre manufacturers.Although it is well known by the tyre industry that the requisitepressure is dependent on the supported load, this load-dependentpressure information is not provided to the driver, since real-time loadis unknown. As a result, should the load vary from that assumed by themanufacturer, the tyres may be improperly inflated. Since the requisitepressure increases with load, the only option left is to assume themaximum load and specify a pressure accordingly. However, this maximumpressure can: 1) give a very hard ride; 2) reduce the tyre-to-roadcontact area available for braking; 3) wear out the center of the tyretread prematurely. Thus, tyre load information is needed to properlyinflate tyres.

Moreover, vehicle electronic control systems, such as for example avehicle brake control system, a traction control system, an anti-lockbraking system, an electronic braking system, a steering control system,an active roll control system, a vehicle stability control system, mayuse information related to the tyre load, in order to control actuatorsthat move, control and stop the vehicle.

This tyre information may be used within the vehicle, or it can be usedremotely, i.e. outside the vehicle. As the telematic capability ofvehicles increases, they are capable of wirelessly communicating with aremote facility for monitoring the vehicle health (diagnostics), forprediction of maintenance (prognostics), and to monitor the vehicle asit passes on the road. The information may be also historicallyimportant to understand the cause of accidents.

U.S. Pat. No. 5,793,285 discloses a method and apparatus for monitoringtyres on a vehicle, by continuously measuring the distance between theassociated vehicle axle (or a vehicle body part rigidly connectedthereto) and the road, while the vehicle is in operation. From thismeasurement, the tyre deflection is determined. According to theauthors, the measured tyre deflection represents a comparatively exactmeasure of the respective tyre load. When the tyre deflection determinedleaves a predetermined desired range, a warning signal is transmitted.

PCT patent application no. WO 03/016115 discloses a method fordetermining the charge or load exerted on a tyre of a motor vehicleand/or for monitoring tyre pressure, wherein the pressure in each tyreis detected during operation of the vehicle and the rotational behaviorof the individual wheels is observed. Load distribution parameters arealso determined by comparing the rotational behavior and/or changes insaid rotational behavior of the individual wheels during given drivingstates, taking into account preset and/or predetermined and/or learnedvariables. Tyre pressure and load distribution parameters are used todetermine the load or charge exerted on the tyres and/or pressure loss.In one example, a pressure-measuring system based on the use of pressuresensors (such as TPMS=Tyre Pressure Measuring System), is used todetermine the tyre pressure, whilst characteristic variablesrepresenting the load distribution are determined using a system basedon an evaluation of wheel speed data operating in the manner of a system(Deflation Detecting System=DDS) used to determine conditions relatingto the dynamic rolling circumferences of the individual tyres.Consequently, the function of detecting capacity utilization can be setup using existing systems. In another example, the number of revolutionsof a front wheel is compared with the number of revolutions of a rearwheel at the same vehicle speed or at approximately the same vehiclespeed (e.g. vehicle reference speed), evaluated to obtain a loaddistribution characteristic variable, and the value and/or the change inthe load distribution characteristic variables in defined drivingsituations is/are used as a means of calculating the capacityutilization or load of the tyres and/or the pressure loss.

US patent application no. 2003/0058118 discloses a vehicle and vehicletyre monitoring system, apparatus and method for determining theload-induced deflection or deformation of a vehicle tyre. Based thereon,deflection-related information, such as tyre load, molar air content,total vehicle mass and distribution of vehicle mass, are provided. Thetyre deflection region or contact region of the loaded tyre is detectedby sensing the acceleration of the rotating tyre by means of anaccelerometer mounted on the tyre, preferably on an inner surface suchas the tread lining thereof. As the tyre rotates and the accelerometeris off of the contact region, a high centrifugal acceleration is sensed.Conversely, when the accelerometer is on the contact region and notrotating, a low acceleration is sensed. The deflection points delimitingthe contact region are determined at the points where the sensedacceleration transitions between the high and low values. From ameasurement of the rotation rate of the tyre, of the time betweendetections of the deflection points and from the tyre radius, thecontact length (contactLength) can be determined. In order to determinethe tyre load, the following formula is suggested:load=α×treadWidth×contactLength×pressure+forceSidewallwhere treadWidth is the width of the tread, treadWidth×contactLength isthe area of applied pressure, forceSidewall is the effective resiliencyof the tyre sidewall to collapse, and α is a proportionality constantnear to 1. Alternatively, the load can be determined from a disclosedrelationship between air moles, pressure, temperature and contactlength, derived from the Ideal Gas Law.

According to the Applicant, the methods disclosed in the above U.S. Pat.No. 5,793,285 and in the above PCT patent application no. WO 03/016115may not give reliable real-time determinations of the tyre load, sincethey are not based on measurements performed directly on the tyre. Thus,they may suffer from an “averaging effect”, which can cause a loss ofimportant tyre load data, especially in rapidly varying conditions.

On the other hand, the approach disclosed in the above US patentapplication no. 2003/0058118 is quite theoretical and could not fit witha complex system such as a tyre. For example, considering the rectangletreadWidth×contactLength as the area of applied pressure is a strongapproximation, as the contact area between the tyre tread and the roadis quite different from a rectangle. Furthermore, the valueforceSidewall is generally not determined with high precision, so that afurther approximation would be included in the tyre load determination.

The Applicant has faced the problem of determining in real-time, i.e.during the running of the vehicle, and in a reliable way, the load towhich a tyre fitted on the vehicle is subjected.

The Applicant has found that such problem can be solved by measuring theamplitude of the deformation in radial direction to which a portion ofthe tread area of the tyre is subjected when such portion passes incorrespondence of the contact region between the tyre and the road, andby relating such amplitude to the rotation speed and to the inflationpressure of the tyre. Hereinafter, the deformation in radial directionwill be referred as “radial deformation”. Such radial deformation can bedetected, for example, by means of a radial accelerometer secured to theinner liner of the tyre.

In a first aspect, the invention relates to a method for determining aload exerted on a tyre fitted on a vehicle during a running of saidvehicle on a rolling surface, the method comprising the following steps:

-   -   acquiring a first signal comprising a first portion        representative of a radial deformation to which a first tread        area portion of said tyre is subjected during passage of said        first tread area portion in a contact region between said tyre        and said rolling surface;    -   measuring an amplitude of said radial deformation in said first        signal portion;    -   estimating a rotation speed and an inflation pressure of said        tyre corresponding to said radial deformation;    -   deriving said tyre load from said amplitude, said rotation speed        and said inflation pressure.

Said first signal may comprise a radial acceleration signal. Said stepof measuring said amplitude can be performed by measuring a differencebetween a maximum value of said first signal and a minimum value of saidfirst signal in said first signal portion.

For the purposes of the present invention, the expression “estimating arotation speed and an inflation pressure of said tyre corresponding tosaid radial deformation” may include either a measurement from which thetyre inflation pressure value and/or the rotation speed value in thetime interval in which the radial deformation of the first tread portionoccurred can be inferred (even if such measurement is performed in asubsequent time interval), or a measurement of the tyre inflationpressure value and/or of the rotation speed value performed in realtime, i.e. during the occurrence of the radial deformation of the firsttread area portion.

The method may further comprise, before said step of measuring saidamplitude, a further step of low-pass filtering said first signal.

Said step of estimating said rotation speed of the tyre may comprisemeasuring an average value of said first signal in a second signalportion, outside from said first signal portion.

Alternatively, said step of estimating said rotation speed of the tyremay comprise measuring an average value of said first signal in a wholeturn of said tyre.

In a preferred embodiment, the method further comprises a step ofacquiring a second signal representative of a radial acceleration towhich a second tread area portion of said tyre is subjected. In suchpreferred embodiment, said step of estimating said rotation speed of thetyre may comprise measuring a value of said second signal during saidpassage of said first tread area portion in said contact region betweensaid tyre and a rolling surface.

The method may further comprise, before said step of measuring saidamplitude, a further step of sampling said first signal at a frequencyof at least 5 kHz, preferably of at least 7 kHz.

The method may further comprise a step of providing characteristicfunctions describing an expected radial deformation amplitude versusrotation speed, corresponding to predetermined conditions of tyre loadand inflation pressure. Said characteristic functions may comprisepolynomial functions.

Preferably, said step of deriving said tyre load may comprise:

-   -   identifying a set of characteristic functions corresponding to        said estimated inflation pressure;    -   determining, from said set of characteristic functions, a        corresponding set of expected radial deformation amplitudes        corresponding to said estimated rotation speed.

More preferably, said step of deriving said tyre load may furthercomprise:

-   -   comparing said measured radial deformation amplitude with any        one of said set of expected radial deformation amplitudes, in        order to identify a closer expected radial deformation        amplitude;    -   determining said tyre load based from said closer expected        radial deformation amplitude.

In a second aspect, the invention relates to a method of controlling avehicle having at least one tyre fitted thereon, comprising:

-   -   determining a load exerted on said tyre by a method according to        the first aspect;    -   passing said determined load to a vehicle control system of the        vehicle;    -   adjusting at least one parameter in said vehicle control system        based on said determined load.

The vehicle control system may comprise a brake control system, and saidstep of adjusting at least one parameter may comprise adjusting abraking force on said tyre.

Alternatively or in combination, the vehicle control system may comprisea steering control system, and said step of adjusting at least oneparameter may comprise selecting a maximum variation allowed fromsteering commands.

Alternatively or in combination, the vehicle control system may comprisea suspension control system, and said step of adjusting at least oneparameter may comprise adjusting a stiffness of a suspension springassociated to said tyre.

Typically, the vehicle comprises at least one tyre fitted on its rightand at least one tyre fitted on its left. Alternatively to or incombination with the previous embodiments, the vehicle control systemmay comprise an active roll control system, and said step of adjustingat least one parameter comprises compensating an unequal loaddistribution between said left fitted tyre and said right fitted tyre.

In a third aspect, the invention relates to a system for determining aload exerted on a tyre fitted on a vehicle during a running of saidvehicle on a rolling surface, the system comprising:

-   -   a measuring device adapted to acquire a signal representative of        a deformation to which a first tread area portion of said tyre        is subjected during passage of said first tread area portion in        a contact region between said tyre and said rolling surface;    -   a pressure sensor adapted to sense an inflation pressure of said        tyre;    -   a device for estimating a rotation speed of said tyre;    -   at least one processing unit being adapted to determine an        amplitude of said radial deformation in said first signal        portion, and to derive said tyre load from said amplitude, said        rotation speed and said inflation pressure.

In a preferred embodiment, said measuring device comprises a radialaccelerometer.

The device for estimating the rotation speed of said tyre may be thesame processing unit.

The system of the invention may further comprise a filtering deviceadapted for low-pass filtering said signal.

The measuring device may further comprise a sampling device adapted tosample said signal at a frequency of at least 5 kHz, preferably of atleast 7 kHz.

At least one memory can be associated to said processing unit. Said atleast one memory may comprise pre-stored characteristic functionsdescribing an expected radial deformation amplitude versus rotationspeed, corresponding to predetermined conditions of tyre load andinflation pressure. Said functions may comprise polynomial functions.

Said at least one memory may further comprise pre-stored instructionsfor said processing unit. Said pre-stored instructions may comprise atleast a first set of instructions being adapted to:

-   -   identify a set of characteristic functions corresponding to a        sensed inflation pressure;    -   determine, from said set of characteristic functions, a        corresponding set of expected radial deformation amplitudes        corresponding to said estimated rotation speed.

Said pre-stored instructions may further comprise at least a second setof instructions being adapted to:

-   -   compare said determined radial deformation amplitude with any        one of said set of expected radial deformation amplitudes, in        order to identify a closer expected radial deformation        amplitude;    -   determine said tyre load based from said closer expected radial        deformation amplitude.

Said measuring device may be included in a sensor device located in atread area portion of said tyre. Preferably, said sensor device may bedisposed substantially in correspondence of an equatorial plane of thetyre.

Preferably, said sensor device may be secured to an inner liner of thetyre. In this embodiment, a damping element may be interposed betweensaid sensor and said inner liner.

The sensor may further comprise a power source. Said power source maycomprise a battery or, preferably, a self-powering device, being adaptedto generate electrical power as a result of mechanical stressesundergone by said sensor device during running of said vehicle. Saidself-powering device may, for example, comprise a piezoelectric element.Furthermore, said self-powering device may comprise an electricalstorage circuit, typically comprising a resistor and a capacitor.

Preferably, the processing unit is included within said sensor device.

Typically, the sensor device further includes a transmitting device.Said transmitting device may be operatively connected to a firstantenna.

The system according to the invention may further comprise a fixed unitlocated on the vehicle, comprising a receiving device for receiving datafrom said sensor device. Said receiving unit typically comprises asecond antenna.

Said first antenna and said second antenna are typically adapted fordata transmission at a frequency comprised between 400 and 450 MHz.

Further features and advantages of the present invention will be betterillustrated by the following detailed description, herein given withreference to the enclosed drawings, in which:

FIG. 1 shows a cross section of a tyre according to the invention,including a sensor device;

FIG. 2 shows a diagram of a fixed unit included in a system according tothe invention;

FIG. 3 shows a diagram of a sensor device included in a tyre accordingto the invention;

FIG. 4 shows a series of radial acceleration curves obtained atdifferent tyre rotation speeds;

FIGS. 5 a and 5 b exemplarily disclose two sets of curves of radialdeformation peak amplitude versus tyre rotation speed, corresponding todifferent tyre loads, respectively for a first and second value of tyreinflation pressure;

FIGS. 6 a and 6 b schematically show a radial deformation signal and afiltered radial deformation signal, respectively;

FIG. 7 shows further sets of curves of radial deformation peak amplitudeversus tyre rotation speed, corresponding to different tyre loads.

FIG. 1 shows a cross section of a wheel comprising a tyre 11 and asupporting rim 12. The tyre 11 shown in FIG. 1 is of a typeconventionally known as “tubeless”, i.e. it does not include an innertube. This tyre can be inflated by means of an inflation valve 13positioned, for example, on the channel of the said rim 12.

The tyre 11 includes a carcass 16, terminating in two beads 14 and 14′,each formed along an inner circumferential edge of the carcass 16, forfixing the tyre 11 to the corresponding supporting rim 12. The beads 14,14′ comprise respective reinforcing annular cores 15 and 15′, known asbead cores. The carcass 16 is formed by at least one reinforcing ply,including textile or metallic cords, extending axially from one bead 14to the other 14′ in a toroidal profile, and having its ends associatedwith a respective bead core 15 and 15′. In tyres of the type known asradial, the aforesaid cords lie essentially in planes containing theaxis of rotation of the tyre. An annular structure 17, known as beltstructure, is placed in a radially external position with respect to thecarcass 16. Typically, the belt structure 17 includes one or more stripsof elastomeric material incorporating metal and/or textile cords,overlapping with each other. A tread band 18 of elastomeric material iswound around the belt structure 17 and impressed with a relief patternfor the rolling contact of the tyre with the ground. Two sidewalls 19and 19′ of elastomeric material, each extending radially outwards fromthe outer edge of the corresponding bead 14 and 14′, are also placed onthe carcass 16 in axially opposed lateral positions. In tubeless tyresthe inner surface of the carcass 16 is normally covered with a liner111, i.e. with one or more layers of air-impermeable elastomericmaterial. Other known elements, such as for example bead fillers may beprovided, according to the specific design of the tyre 11.

A sensor device 3, that will be described in detail in the remainder ofthe description, is included within the tyre 11. The sensor device 3 islocated in a portion of the tread area of the tyre 11, i.e. the regionof the tyre 11 axially extended between the sidewalls of the tyre 11.Preferably, the sensor device is disposed substantially incorrespondence of the equatorial plane of the tyre 11. In the preferredembodiment shown in FIG. 1, the sensor device 3 is secured to the innerliner 111 of the tyre 11. A fixing element 332 adheres both to thesensor device 3 and to the inner liner 111. Suitable materials for thefixing element 332 may include generally flexible rubbers, such as forexample natural rubber, or synthetic rubber, e.g. rubbers made fromconjugated dienes having from 4 to 10 carbon atoms such aspoly-isoprene, polybutadiene, styrene-butadiene rubber and the like. Inpreferred embodiments, a material included in the fixing element 332should have a damping effect, in order to secure the fixing of thesensor device 3 to the inner surface of the tyre by minimizing themechanical stresses exerted onto the fixing surface during use of thetyre 11. Furthermore, a damping material reduces the probability ofdamages to the sensor device 3 by preventing transmission of the abovestresses to the device. Suitable damping materials may have a Shore Ahardness (measured at 23° C. according to ASTM Standard D2240) of fromabout 1 to about 40, and an elastic rebound (measured at 23° C.according to ASTM Standard D1054) lower than about 60. Cross-linkeddiene elastomers or polyurethane gel materials may be adapted in orderto fit with these damping specifications. For improved adhesion betweenthe sensor device 3 and the tyre 11, it may be advantageous to interposea further adhesive element, for example a double-sided adhesive film,between the fixing element 332 and the inner surface of the tyre 11and/or between the fixing element 332 and the sensor device 3. Anappropriate double-sided adhesive film may be the Scotch® 300SL HIStrength, marketed by 3M. In alternative embodiments, the sensor device3 may be incorporated within the structure of the tyre in the treadarea, for example within the tread band, or between the outer belt stripand the tread band.

In a preferred embodiment of the present invention (not shown), aplurality of sensor devices are associated to a tyre 11. Moreparticularly, the sensor devices may be located in a circumferentialposition spaced one from each other of substantially the same angle. Forexample, three sensor devices may be located within the tyre,circumferentially spaced from each other of an angle of substantially120°. As far as the securing of the plurality of the sensor devices tothe tyre 11, reference is made to what said above.

As it will be clarified in the following, the use of a plurality ofsensor devices allows to achieve more accuracy and reliability of themeasurements performed, as well as a better monitoring of the tyre loadduring the entire wheel turn.

The sensor device 3 is adapted to communicate with a unit external tothe tyre 11. Such external unit will be referred in the following as“fixed” unit. Typically, the fixed unit may be located on the vehicle onwhich the tyre 11 is fitted. Alternatively or in combination with afixed unit located on the vehicle, a fixed unit may be a hand-held unitusable by an operator, or a unit located along a roadway (e.g. in aservice station).

For example, FIG. 2 shows a block diagram of a fixed unit 2, comprisinga device for receiving from the sensor device 3 included within the tyre11. Preferably, the fixed unit 2 also comprises a device fortransmitting to said sensor device 3. The receiving device may comprisea radio-frequency receiver 26 connected to a first antenna 25, referredto below as the “fixed antenna”. Preferably, the receiving device alsocomprises an electrical demodulator device 27. A memory 28, such as forexample an EPROM, can store the data received by the sensor device 3 anddemodulated by the demodulator 27. In preferred embodiments, the memory28 is associated to a central processing unit (CPU, not shown in FIG.2), in order to perform calculations from the data received by thesensor device 3 and/or stored in the memory 28. The memory 28 may alsostore historical logs of excessive tyre loads, pressure and/ortemperatures, possibly in combination with logs of the steps taken by avehicle control system in order to control the vehicle behavior and/orof alarm messages displayed to the driver of the vehicle. Thetransmission device preferably comprises an oscillator circuit 23, whichsupplies a driver circuit 24 for the fixed antenna 25. If the fixed unit2 is located on the vehicle, the electrical energy required to power thefixed unit 2 can be supplied directly by the vehicle battery.

The sensor device 3, an exemplary block diagram of which is shown inFIG. 3, comprises in general terms a device 31 for data transmission tothe said fixed unit and a measuring device 32 adapted to measure aradial deformation of the tread area portion of the tyre 11 to which thesensor device 3 is associated. The measuring device 32 may preferablycomprise a radial accelerometer. Such radial accelerometer should becapable of support and correctly measure very high acceleration values,as the radial acceleration supported by the tread area of the tyre mayreach, at high speed, values of 500-1000 g, wherein g is the gravityacceleration. In an alternative embodiment, the measuring device maycomprise an extensometer, whose output signal gives a measure of theflexion of the monitored tread area portion. The load to which the tyreis subjected is determined by measuring the amplitude of the radialdeformation to which the tread area portion corresponding to theposition of the sensor device 3 is subjected. For the purposes of thepresent invention, the expression “radial deformation” may compriseeither the actual tyre deflection (for example measured in mm, or as aratio to the tyre radius) to which the monitored tread area portion issubjected, or the radial acceleration to which the monitored tread areaportion is subjected. In order to perform a real-time determination ofthe tyre load, the radial deformation should be detected with highprecision, preferably at any turn of the tyre. For this purpose, andtaking into account the frequency rotation of a rolling tyre(particularly at high speed), the measuring device 32 preferablyincludes a sampling device (not shown) capable of enabling the readingof the sensed radial deformation signal at a frequency of at least 5kHz, more preferably at a frequency of at least 7 kHz, so as to furnisha sampled signal thereof. In preferred embodiments, the measuring device32 may also include a pressure sensor and/or a temperature sensor.However, pressure and temperature measurements do not need a highfrequency sampling: a single measure per tyre turn may be sufficient. Inalternative embodiments, a pressure and/or a temperature sensor may alsobe disposed externally of the sensor device 3, e.g. located within thetyre valve. The sensor device 3 typically includes also an antenna 37,referred to below as the “mobile antenna”, operatively connected to saidtransmission device 31, for data transmission to the fixed antenna ofthe fixed unit. Transmission from the mobile antenna to the fixedantenna may occur at conventional telemetry radio-frequencies, e.g. in aband comprised between 400 and 450 MHz (for example at 418 MHz or 433MHz).

The sensor device 3 may further include a processing unit (CPU) 34,associated to a memory device 35. This memory device 35 may containre-writable memory locations in which information about the measurementstaken by the measuring device 32 can be stored. Furthermore, it may alsocontain pre-stored instructions for the processing unit 34, suitable forpre-processing the signals coming from the measuring unit 32 beforetransmission, in order to reduce the quantity of information sent out ofthe tyre 11. More particularly, the deformation signal may bepre-processed in order to detect characteristic points, such as forexample maxima and minima, the coordinates of which can be sent to thetransmission device 31 for transmission to the fixed unit. This allowsto save transmission bandwidth and required power for transmission.Furthermore, a filtering device (not shown) may be interposed betweenthe measuring unit 32 and the processing unit 34, in order to low-passfilter the deformation signal and discriminate the useful signal fromhigh-frequency noise caused by the interaction between the tread bandand the road. However, such filtering may be provided by electronicsincluded within the measuring device 32 or as further pre-processinginstruction stored within the memory 35.

A power source 33 allows to energize the sensor device 3. The sensordevice 3 may be powered by a battery. However, for a real-timedetermination of the tyre load a great electrical power consumption maybe requested by the measuring device 32 (in particular by a highfrequency sampling device), by the processing unit 34 and by thetransmission device 31, so that a battery could have short lifetime, ascompared to the entire life of the tyre. Thus, in preferred embodimentsthe power source 33 includes a self-powering device, which generateselectricity as a result of the mechanical stresses to which saidself-powering device is subjected (for example, centrifugal force, orthe deformations of the liner, or movements due to traveling on unevenroads). As an example, piezoelectric materials may be used in theself-powering device for such purpose. The self-powering device alsoincludes an electrical energy storage circuit (not shown), typicallyincluding a resistor and a capacitor. As a further alternative, thesensor device 3 may be energized by the fixed unit by means of asuitable receiving device (not shown), connected to the mobile antenna31.

A device for distributing the electrical power 36 preferably distributesappropriately the electrical power provided by the power source 33 tosaid processing unit 34, to said memory device 35, to said device fortransmitting 31 and to said measuring device 32, according to theirrequirements.

It has to be noticed that it is not necessary to include the measuringdevice, the transmission portion to the fixed unit and the controlelectronics within a single packaged sensor device. For example, thecontrol electronics and the transmission portion to the fixed unit couldbe packaged in a separated device secured to other parts of the tyre orof the wheel (e.g. the rim, or the sidewall), associated by a wired orwireless (e.g. optical or by radio-frequency) connection to a measuringdevice located in the tread area portion of the tyre.

FIG. 4 shows, by way of example, the result of a series of measurementsperformed by the Applicant by securing a radial accelerometer to theinner liner of a tyre model Pirelli® P6000® 195/65 R15, inflated at apressure of 2.2 bar, with a load of 3500 N. A rolling of the tyre wascaused at different speeds and the radial acceleration signal detectedby the accelerometer was correspondingly plotted. In FIG. 4, therotation angle R for a single turn around the tyre axis of the treadarea portion corresponding to the accelerometer position is reported inabscissa. The angle ranges from 0° to 360°, these two extremescorresponding substantially to a radially opposite position with respectto the contact region between the tyre and the road (hereinafter contactpatch). On the contrary, the position around 180° corresponds to thepassage of the crown portion monitored by the accelerometer under thecontact patch. The radial acceleration a sensed by the accelerometer isreported in ordinate, as a multiple of g. Curve 41 refers to a travelingspeed of 40 km/h, curve 42 refers to a traveling speed of 60 km/h, curve43 refers to a traveling speed of 80 km/h, curve 44 refers to atraveling speed of 100 km/h. As it can be seen, in correspondence to thepassage under the contact patch the level of radial centrifugalacceleration sensed by the accelerometer increases abruptly a firsttime, then drops to until substantially zero, and then increasesabruptly a second time. In other positions the radial accelerationsensed by the accelerometer has an average level related to the rotationspeed of the rolling tyre: the higher the speed, the higher the sensedacceleration. The curves of FIG. 4 show that when the tread area portioncorresponding to the position of the accelerometer begins and ends itspassage under the contact patch, such tread area portion is subjected toa strong radial deformation (corresponding to the peaks shown by thecurves), whereas in other positions such tread area portion is notpractically subjected to deformations (corresponding to thesubstantially zero acceleration value within the contact patch and tothe substantially constant acceleration value outside from the contactpatch).

By analyzing radial acceleration curves in different conditions ofrotation speed, load and inflation pressure, the Applicant has observedthat:

-   a) the amplitude of the peaks representing the radial deformation of    the tread area portion increases with increasing rotation speed of    the tyre (i.e., the higher the speed, the higher the peaks);-   b) at constant speed, the amplitude of the peaks representing the    radial deformation of the tread area portion increases with    increasing tyre load (i.e., the higher the load, the higher the    peaks);-   c) at constant speed, the amplitude of the peaks representing the    radial deformation of the tread area portion decreases with    increasing tyre inflation pressure (i.e., the higher the pressure,    the lower the peaks).

Summarizing the above results, the Applicant has plotted differentcurves of radial deformation (peak) amplitude versus rotation speed,corresponding to different tyre loads, on the same graph, at constantinflation pressure. FIGS. 5 a, 5 b show two of such plots, carryingcurves of peak amplitude versus tyre rotation speed increasing tyreloads (the arrow shown in the figures refers to increasing tyre loads).FIGS. 5 a, 5 b relate to an inflation pressure of 1.6 bar (FIG. 5 a) and2.2 bar (FIG. 5 b). As each curve represents a predetermined tyre loadvalue, by knowing the rotation speed and the inflation pressure, and bymeasuring the radial deformation peak amplitude value, a unique curverepresenting a tyre load value can be identified in the graph, i.e. thetyre load can be estimated.

On the other hand, since a_(radial)=V²/R or a_(radial)=ω²R (wherein R isthe radius of the tyre), the average level of acceleration to which thetread area portion corresponding to the position of the radialaccelerometer is subjected outside the contact patch increases withincreasing rotation speed, substantially without any dependency on thetyre load and inflation pressure. This means that the rotation speed ofthe tyre can be derived by measuring the average radial accelerationlevel in the portion of the radial acceleration signal corresponding tothe outside of the contact patch, for any tyre load and inflationpressure. Thus, advantageously, a signal furnished by a radialaccelerometer disposed in a tread area portion of the tyre can give twoof the parameters needed for estimating the tyre load, i.e. theamplitude of the radial deformation peak and the rotation speed. Thethird parameter, i.e. the inflation pressure, can be provided by aconventional pressure sensor. However, it has to be noticed that alsothe tyre rotation speed may be provided by a separate device, such asfor example by a measurement performed in other parts of the vehicle,different from the tyre (e.g., the wheel hub).

In a preferred method for determining the tyre load, each of the curvesshown in FIGS. 5 a, 5 b can be described by a fit function, such as forexample a polynomial fit function. For example, the curves obtained at apressure p and at different tyre loads q1, q2, . . . qn can be describedby parabolic fit functions: $\begin{matrix}{{{{y\_}1} = {{a\quad 1_{{q\quad 1},p}\omega^{2}} + {b\quad 1_{{q\quad 1},p}\omega} + {c\quad 1_{{q\quad 1},p}}}}{{{y\_}2} = {{a\quad 2_{{q\quad 2},p}\omega^{2}} + {b\quad 2_{{q\quad 2},p}\omega} + {c\quad 2_{{q\quad 2},p}}}}\cdots\cdots{{y\_ n} = {{a\quad n_{{qn},p}\omega^{2}} + {b\quad n_{{qn},p}\omega} + {c\quad n_{{q\quad 2},p}}}}} & \lbrack 1\rbrack\end{matrix}$

The values y_(—)1(q, p, ω), . . . , y_n(q, p, ω) calculated withequations [1] represent expected radial deformation peak values, atgiven conditions of tyre load, pressure and rotation speed.

In an initial step of characterization of a tyre, graphs similar tothose shown in FIGS. 5 a and 5 b can be plotted for the tyre atpredetermined inflation pressure values p1, p2 . . . pn, predeterminedtyre loads q1, q2, . . . . qn, and predetermined rotation speeds, inorder to find the sets of fit coefficients for the above values ofinflation pressure, i.e. $\begin{matrix}{{{{pressure}\quad p\quad 1\text{:}\quad( {{a\quad 1_{{q\quad 1},{p\quad 1}}},{b\quad 1_{{q\quad 1},{p\quad 1}}},{c\quad 1_{{q\quad 1},{p\quad 1}}}} )},\ldots\quad,( {{a\quad n_{{q\quad n},{p\quad 1}}},{b\quad n_{{q\quad n},{p\quad 1}}},{c\quad n_{{q\quad n},{p\quad 1}}}} )}{{{pressure}\quad p\quad 2\text{:}\quad( {{a\quad 1_{{q\quad 1},{p\quad 2}}},{b\quad 1_{{q\quad 1},{p\quad 2}}},{c\quad 1_{{q\quad 1},{p\quad 2}}}} )},\ldots\quad,( {{a\quad n_{{q\quad n},{p\quad 2}}},{b\quad n_{{q\quad n},{p\quad 2}}},{c\quad n_{{q\quad n},{p\quad 2}}}} )}\cdots\cdots{{{pressure}\quad p\quad n\text{:}\quad( {{a\quad 1_{{q\quad 1},{p\quad n}}},{b\quad 1_{{q\quad 1},{p\quad n}}},{c\quad 1_{{q\quad 1},{p\quad n}}}} )},\ldots\quad,( {{a\quad n_{{q\quad n},{p\quad n}}},{b\quad n_{{q\quad n},{p\quad n}}},{c\quad n_{{q\quad n},{p\quad n}}}} )}} & \lbrack 2\rbrack\end{matrix}$

The fit coefficients [2], as well as the pressure values to which theyare related, can be stored within the memory included within the sensordevice 3 located in the tread area of the tyre. The above describedcharacterization of the tyre can be performed once per tyre model, forexample in indoor tests.

With reference to FIG. 6, during running of the tyre, a signalrepresentative of the radial acceleration to which a tread area portionis generated by the radial accelerometer secured to the tyre (see FIG.6(a)). The signal can be low-pass filtered, in order to removehigh-frequency components due to interaction between the road and thetyre (see FIG. 6(b)). From the filtered signal, the amplitude Pp of thesignal peak can be measured. Preferably, the peak amplitude value to bemeasured corresponds to the difference between the maximum signal valueand the minimum signal value. Furthermore, the amplitude correspondingto the first peak can be used, or the amplitude of the second peak, oran average of the first and of the second peak.

In order to derive the rotation speed of the tyre, the averageacceleration level a in a portion outside the signal variation caused bythe passage of the accelerometer under the contact patch can also bemeasured. The radius of the tyre should also be known for the abovepurpose. In an alternative embodiment, the average signal value in awhole turn of the tyre could be used as a measure of the averageacceleration level a. In a further alternative embodiment, using aplurality of sensor devices located within the tyre at differentcircumferential positions, a first sensor device located outside thecontact patch could be used in order to measure the average accelerationlevel a (and derive the rotation speed of the tyre), in real-time, inthe same time interval in which a second sensor device passes under thecontact patch. Simple control electronics can be implemented within thesensor devices in order to trigger the needed measurements. The neededalgorithms for the above described analysis of the signal generated bythe accelerometer can also be stored within the memory of the sensordevice, in order to be used by the associated processing unit.

The pressure p is also measured during running of the tyre. By using themeasured pressure p, the correct set of fit coefficients of the tyreload curves can be identified (see equations [2]). Should the measuredpressure px be different from the pressure values p1, p2, . . . pn usedfor the characterization of the tyre, a corrective factor can beapplied. Let, for example, p1 be the closer stored pressure value to px,then the corrective factor may be γ=px/p1, so as the corrected fitcoefficients take the following values:pressure px: [(a1_(q1,p1))^(γ), (b1_(q1p1))^(γ), (c1_(q1p1))^(γ)], . . ., [(an_(qn,p1))^(γ), (bn_(qn,p1))^(γ), (cn_(qn,p1))^(γ])

Then, by using the measured rotation speed V_(m) (or ω_(m)) and theidentified fit coefficients, different expected radial deformation peakvalues y_(—)1(ω_(m), q1, px), y_(—)2(ω_(m), q2, px), . . . , y_n(ω_(m),qn, px) can be determined. Such values y_(—)1, y_(—)2, . . . , y_n arethen compared with the measured peak amplitude Pp, in order to thedetermine the closer value thereof. Such closer value identifies thecloser tyre load curve, i.e. the closer tyre load to the actual loadsupported by the tyre. The identification of the closer tyre load curvecould be enough for an estimation of the tyre load, depending on therequirements. For a more precise determination, a simple proportion canbe performed in order to determine the actual tyre load. Lety_(—)3(ω_(m), q3, px) be the closer expected peak amplitude valuecalculated at px and V_(m)(or ω_(m)), identifying the closer tyre loadq3. Thus, it holds:actual tyre load: Pp=q3:y_(—)3and then:actual tyre load=Pp×q3/y _(—)3  [3]

The above described formulas for calculation of the actual tyre load canalso be stored within the memory of the sensor device, in order to beused by the associated processing unit.

EXAMPLE

The Applicant has performed a series of measurements by using a radialaccelerometer secured to the inner liner of a tyre model Pirelli® P7®,having a radius of 0.31 m. FIG. 7 shows a plot with four curves of theradial deformation peak values measured during the characterizationstep, versus the rotation speed of the tyre. The four curves shown inFIG. 7 refer to measurements performed at an inflation pressure of 2.2bar, and at the following tyre loads: tyre loads of 250 kg, 300 kg, 450kg, 600 kg. As above described, higher tyre loads correspond to highercurves (i.e., to higher peak values). In particular, the four curvesshown in FIG. 7 can be described by the following fit functions:y _(—)1=0.034 ω²+0.031 ω+0.27 for q1=250 kgy _(—)2=0.041 ω²+0.049 ω+0.30 for q2=300 kgy _(—)3=0.049 ω²+0.053 ω+0.23 for q3=450 kgy _(—)4=0.055 ω²+0.030 ω+0.29 for q4=600 kg  [4]

After the characterization, a measurement at a tyre load different fromthe above values was performed. From the radial acceleration signal, aradial deformation peak amplitude value of 210 g and a rotation speed of75 km/h were derived. The inflation pressure was 2.2 bar.

By using equations [4], the following expected deformation peakamplitudes can be calculated at a rotation speed of 75 km/h: y_(—)1=156g; y_(—)2=189 g; y_(—)3=225 g y_(—)4=251 g. Thus, the closer peakamplitude value is y_(—)3, corresponding to a tyre load of 450 kg. Byusing equation [3], it could be derived the actual tyre load, i.e. 420kg.

It has to be understood that the above described method for determiningthe tyre load could be modified without departing from the generalteachings of the invention. For example, a database comprising values ofexpected radial deformation peaks corresponding to predetermined tyreinflation pressures, tyre rotation speeds and tyre loads intervals canbe stored within the memory of the sensor device 3, in place of theabove mentioned fit coefficients. The values stored in the databasecould be inferred by characterization curves obtained as disclosedabove. From such database, an estimation of the tyre load could be done,after having gained knowledge of the radial deformation amplitude, ofthe tyre rotation speed and of the tyre inflation pressure.

The real-time determination of the load acting on a tyre mounted on avehicle is an important parameter that can be passed to a vehiclecontrol system, in order to control the behavior of the vehicle,particularly in critical conditions. A vehicle control system maycomprise a brake controller (for example, an anti-lock brake unit),and/or a steering controller, and/or a suspension controller, and/or anengine controller, and/or a transmission controller.

For example, a vehicle brake control system may adjust the braking forceon each tyre according to the load on the tyre.

As another example, the loads on each tyre may be used to determine thevehicle stability envelope and to select the maximum variation allowedfrom steering commands. This information may be applicable to a steeringcontrol system (Electrically Assisted Steering Systems) to limit the yawrate.

As another example, a vehicle suspension control system may adjust thestiffness of the suspension springs for each tyre according to the loadon the tyre. Furthermore, a sensed unequal load distribution betweenleft fitted tyres and right fitted tyres could be compensated by anActive Roll Control system, that currently use sensed lateralacceleration to increase the hydraulic pressure to move stabilizer bars,in order to remove a vehicle lean when cornering.

The conditions of the vehicle may indicate that the performance of thevehicle is reduced and that the driver should restrict his drivingmaneuvers. The vehicle control system itself can take action, forexample in order to limit the maximum vehicle speed to maintainstability and not exceed the tyre specifications, or to limit steeringyaw rate in order to keep rollovers from occurring. The driver may bealerted to the current vehicle control system condition and of theactions that the vehicle control system has taken on his behalf to safethe vehicle (reducing the maximum attainable speed, steering rate,engine power), as needed on a display device. On the same display deviceit may also be shown whether he should take further action on his own(change the distribution of mass, restrict driving maneuvers and speed).The display device may comprise a visual and/or an audible unit, forexample located in the dashboard of the vehicle.

1-47. (canceled)
 48. A method for determining a load exerted on a tyre,fitted on a vehicle, during running of the vehicle on a rolling surface,the method comprising: acquiring a first signal comprising a firstsignal portion representative of a radial deformation; measuring anamplitude of the radial deformation in the first signal portion;estimating a rotation speed of the tyre corresponding to the radialdeformation; estimating an inflation pressure of the tyre correspondingto the radial deformation; and deriving the load exerted on the tyrefrom the amplitude, the rotation speed, and the inflation pressure;wherein the first signal portion is representative of the radialdeformation to which a first tread area portion of the tyre is subjectedduring passage of the first tread area portion through a contact regionbetween the tyre and the rolling surface.
 49. The method of claim 48,wherein the first signal comprises a radial acceleration signal.
 50. Themethod of claim 48, wherein measuring the amplitude of the radialdeformation comprises measuring a difference between: a maximum value ofthe first signal in the first signal portion; and a minimum value of thefirst signal in the first signal portion.
 51. The method of claim 48,further comprising: low-pass filtering the first signal before measuringthe amplitude of the radial deformation.
 52. The method of claim 48,wherein estimating the rotation speed of the tyre comprises: measuringan average value of the first signal in a second signal portion; whereina time period associated with the second signal portion does not overlapa time period associated with the first signal portion.
 53. The methodof claim 48, wherein estimating the rotation speed of the tyre comprisesmeasuring an average value of the first signal corresponding to anentire revolution of the tyre.
 54. The method of claim 48, furthercomprising: acquiring a second signal representative of a radialacceleration to which a second tread area portion of the tyre issubjected.
 55. The method of claim 54, wherein estimating the rotationspeed of the tyre comprises: measuring a value of the second signalduring passage of the first tread area portion through the contactregion between the tyre and the rolling surface.
 56. The method of claim48, further comprising: sampling the first signal at a frequency greaterthan or equal to 5 kHz before measuring the amplitude of the radialdeformation.
 57. The method of claim 48, further comprising: samplingthe first signal at a frequency greater than or equal to 7 kHz beforemeasuring the amplitude of the radial deformation.
 58. The method ofclaim 48, further comprising: providing characteristic functionsdescribing an expected radial-deformation amplitude versus rotationspeed that correspond to predetermined conditions of load exerted on thetyre and inflation pressure.
 59. The method of claim 58, wherein thecharacteristic functions comprise polynomial functions.
 60. The methodof claim 58, wherein deriving the load exerted on the tyre comprises:identifying a set of characteristic functions corresponding to theestimated inflation pressure; and determining, from the set ofcharacteristic functions, a corresponding set of expectedradial-deformation amplitudes corresponding to the estimated rotationspeed.
 61. The method of claim 60, wherein deriving the load exerted onthe tyre further comprises: comparing the measured radial-deformationamplitude with any one of the set of expected radial-deformationamplitudes in order to identify a closest expected radial-deformationamplitude; and establishing the load exerted on the tyre based on theclosest expected radial-deformation amplitude.
 62. A method ofcontrolling a vehicle having at least one tyre fitted on the vehicle,the method comprising: determining a load exerted on the at least onetyre; passing the determined load to a vehicle control system of thevehicle; and adjusting at least one parameter in the vehicle controlsystem based on the determined load; wherein the load exerted on the atleast one tyre is determined by a method comprising: acquiring a firstsignal comprising a first signal portion representative of a radialdeformation; measuring an amplitude of the radial deformation in thefirst signal portion; estimating a rotation speed of the at least onetyre corresponding to the radial deformation; estimating an inflationpressure of the at least one tyre corresponding to the radialdeformation; and deriving the load exerted on the at least one tyre fromthe amplitude, the rotation speed, and the inflation pressure; andwherein the first signal portion is representative of the radialdeformation to which a first tread area portion of the at least one tyreis subjected during passage of the first tread area portion through acontact region between the at least one tyre and a rolling surface. 63.The method of claim 62, wherein the vehicle control system comprises: abrake control system; wherein adjusting the at least one parametercomprises adjusting a braking force on the at least one tyre.
 64. Themethod of claim 62, wherein the vehicle control system comprises: asteering control system; wherein adjusting the at least one parametercomprises selecting a maximum variation allowed from steering commands.65. The method of claim 62, wherein the vehicle control systemcomprises: a suspension control system; wherein adjusting the at leastone parameter comprises adjusting stiffness of a suspension springassociated with the at least one tyre.
 66. The method of claim 62,wherein the vehicle comprises at least one tyre fitted on each of twoopposite sides of the vehicle, wherein the vehicle control systemcomprises an active roll control system, and wherein adjusting the atleast one parameter comprises compensating an unequal load distributionbetween the at least one tyre fitted on each of two opposite sides ofthe vehicle.
 67. A system for determining a load exerted on a tyre,fitted on a vehicle, during running of the vehicle on a rolling surface,the system comprising: a measuring device; a pressure sensor; a devicefor estimating a rotation speed of the tyre; and at least one processingunit; wherein the measuring device is adapted to acquire a signalrepresentative of a deformation to which a first tread area portion ofthe tyre is subjected during passage of the first tread area portionthrough a contact region between the tyre and the rolling surface,wherein the pressure sensor is adapted to sense an inflation pressure ofthe tyre, wherein the at least one processing unit is adapted todetermine an amplitude of a radial deformation in a first portion of thesignal, and wherein the at least one processing unit also is adapted toderive the load exerted on the tyre from the rotation speed, theinflation pressure, and the amplitude.
 68. The system of claim 67,wherein the measuring device comprises: a radial accelerometer.
 69. Thesystem of claim 67, wherein the measuring device comprises: a samplingdevice; wherein the sampling device is adapted to sample the signal at afrequency greater than or equal to 5 kHz.
 70. The system of claim 67,wherein the measuring device comprises: a sampling device; wherein thesampling device is adapted to sample the signal at a frequency greaterthan or equal to 7 kHz.
 71. The system of claim 67, further comprising:at least one memory; wherein the at least one memory is associated withthe at least one processing unit.
 72. The system of claim 71, whereinthe at least one memory comprises: pre-stored characteristic functions;wherein the pre-stored characteristic functions describe an expectedradial-deformation amplitude versus rotation speed that corresponds topredetermined conditions of load exerted on the tyre and inflationpressure.
 73. The system of claim 72, wherein the pre-storedcharacteristic functions comprise polynomial functions.
 74. The systemof claim 71, wherein the at least one memory comprises pre-storedinstructions for the at least one processing unit.
 75. The system ofclaim 74, wherein the pre-stored instructions comprise at least onefirst set of instructions adapted to: identify a set of characteristicfunctions corresponding to a sensed inflation pressure; and determine,from the set of characteristic functions, a corresponding set ofexpected radial-deformation amplitudes corresponding to the estimatedrotation speed.
 76. The system of claim 75, wherein the pre-storedinstructions comprise at least one second set of instructions adaptedto: compare the determined radial-deformation amplitude with any one ofthe set of expected radial-deformation amplitudes in order to identify aclosest expected radial-deformation amplitude; and establish the loadexerted on the tyre based on the closest expected radial-deformationamplitude.
 77. The system of claim 67, wherein the measuring device isincluded in a sensor device disposed in a tread area portion of thetyre.
 78. The system of claim 77, wherein the sensor device is disposednear an equatorial plane of the tyre.
 79. The system of claim 77,wherein the sensor device is secured to an inner liner of the tyre. 80.The system of claim 79, further comprising: a damping element betweenthe sensor and the inner liner.
 81. The system of claim 77, wherein thesensor device comprises a transmitting device.
 82. The system of claim81, wherein the transmitting device is operatively connected to a firstantenna.
 83. The system of claim 67, further comprising: a filteringdevice; wherein the filtering device is adapted for low-pass filteringthe signal.
 84. The system of claim 77, wherein the sensor devicefurther comprises a power source.
 85. The system of claim 84, whereinthe power source comprises a battery.
 86. The system of claim 84,wherein the power source comprises: a self-powering device; wherein theself-powering device is adapted to generate electrical power as a resultof mechanical stresses undergone by the sensor device during the runningof the vehicle.
 87. The system of claim 86, wherein the self-poweringdevice comprises a piezoelectric element.
 88. The system of claim 86,wherein the self-powering device comprises an electrical storagecircuit.
 89. The system of claim 88, wherein the electrical storagecircuit comprises: a resistor; and a capacitor.
 90. The system of claim77, wherein the sensor device comprises the at least one processingunit.
 91. The system of claim 77, further comprising: a fixed unitlocated on the vehicle; wherein the fixed unit comprises a receivingdevice for receiving data from the sensor device.
 92. The system ofclaim 91, wherein the sensor device further comprises: a transmittingdevice; wherein the transmitting device is operatively connected to afirst antenna, and wherein the receiving device comprises a secondantenna.
 93. The system of claim 92, wherein the first and secondantennas are adapted for data transmission at a frequency greater thanor equal to 400 MHz and less than or equal to 450 MHz.
 94. The system ofclaim 67, wherein the device for estimating the rotation speed of thetyre is the at least one processing unit.